Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 221152
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
652 AM CDT Sat Apr 22 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 339 AM CDT Sat Apr 22 2017

One wave of rain will move out of the area around 10z while the next
wave moves into central MO. Previous forecast has a decent handle on
the situation however have had to manipulate the pops a bit to try
and match the movement. Temperatures will be quite cool today, but
have raised the highs just a bit for most areas. The upper system
finally moves out late tonight from 06 to 12z Sunday. Rain will end
this evening hanging on the longest across the southeast. Plenty of
dry air, sunshine, and warmer temperatures for Sunday.

JPK

.LONG TERM...  (Sunday through Friday)
Issued at 339 AM CDT Sat Apr 22 2017

After a chilly start to Sunday morning strong April sunshine under a
mostly clear sky should kick temperatures back up into the upper 60s
and low 70s in spite of continuing weak north-northeast flow and cold
advection.  Tranquil weather continues Sunday night through Monday
night with temperatures warming well into the 70s on Monday as warm
advection ramps back up ahead of a trof of low pressure over the
Great Plains.

The cold front associated with this trof will move into southeast
Nebraska or northwest Missouri on Tuesday.  There`s some
discrepancies between model guidance on the timing and strength of
the system as it pushes further east through Missouri on Tuesday
night.  It does look like we`ll see some thunderstorms Tuesday night
across the area.  GFS has MUCAPE over 500 J/Kg all the way up into
west central Illinois at 06Z with showalter index around -3...though
the greatest instability will stay south of I-70 across southeast
Missouri and southwest Illinois with MUCAPE in excess of 1000 J/Kg.
0-6km shear is 40-50kts and the greater instability across the
Ozarks suggests there could be some strong to severe storms. However
the ECMWF is has even less CAPE than the GFS and would suggest that
severe potential would be very limited if any at all Tuesday night.
The ECMWF is also quite a bit faster pushing the front through and
would basically have us in dry/cold advection all day Wednesday
while the GFS pushes the front through our area during the morning
and early afternoon on Wednesday and therefore has much more
precipitation over us.  Tuesday continues to look warm ahead of the
front int warm advection. Think upper 70s and low 80s is easily
attainable in southwest flow. Wednesday should be cooler whether due
to clouds and precip or due to cold advection.

The GFS drops another strong longwave trof of low pressure over the
Rockies on Thursday.  The ECMWF handles this trof differently with
an initially weaker shortwave and then the stronger longwave
developing late in the forecast on Friday.  Either way, the weather
on Thursday and particularly Friday looks unsettled although
confidence is low due to the model differences that far out.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 645 AM CDT Sat Apr 22 2017

VFR conditions will generally prevail with the exception of some
MVFR in the St. louis area due to brief downpours rain and a
period of marginal clouds. UIN and COU look to stay VFR as the
upper system will move a bit south and to eastern MO by 00z. The
trend has been for the precipitation to occur on the southern side
of the system with I-70 be a rough border. VFR wil prevail across
the entire area for Sunday as surface high pressure and much drier
air moves in.

SPECIFICS FOR KSTL: Expect a period of MVFR this morning with some
heavier tsra/shra. Although there is no lightning showing up now
there was some earlier so it is prudent to have tsra as the
heavier band moves through by 13z. MVFR clouds may prevail for a
couple of hours this morning with VFR returning by midday and
continuing through Sunday.

JPK

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     55  43  72  48 /  90  20   0   0
Quincy          59  40  71  45 /  20  10   0   0
Columbia        56  40  70  44 /  80  10   0   0
Jefferson City  56  41  70  43 /  90  10   0   0
Salem           54  42  68  44 /  80  30   0   0
Farmington      49  42  68  42 /  90  40   0   0

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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